Enable dual-stack on all platform with exception for OpenBSD

src/aioquic/asyncio/client.py

@@ -1,5 +1,6 @@
 import asyncio
 import socket
+import sys
 from contextlib import asynccontextmanager
 from typing import AsyncGenerator, Callable, Optional, cast
 
@@ -59,11 +60,23 @@ async def connect(
         token_handler=token_handler,
     )
 
+    # OpenBSD well known to not support dual-stack
+    dual_stack = not sys.platform.startswith('openbsd')
+
+    # Use AI_ADDRCONFIG on platforms which doesn't support dual-stack
+    getaddr_flags = 0
+    if not dual_stack:
+        getaddr_flags = socket.AI_ADDRCONFIG
+
     # lookup remote address
-    infos = await loop.getaddrinfo(host, port, type=socket.SOCK_DGRAM, flags=socket.AI_ADDRCONFIG)
+    infos = await loop.getaddrinfo(host, port, type=socket.SOCK_DGRAM, flags=getaddr_flags)
 
     addr = infos[0][4]
     # addr is 2-tuple for AF_INET and 4-tuple for AF_INET6
+    if dual_stack and len(addr) == 2:
+        addr = ("::ffff:" + addr[0], addr[1], 0, 0)
+        local_tuple = ("::", local_port, 0, 0)
+        sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
     if len(addr) == 2:
         local_tuple = ("0.0.0.0", local_port)
         sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
@@ -75,6 +88,8 @@ async def connect(
 
     completed = False
     try:
+        if dual_stack:
+            sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
         sock.bind(local_tuple)
         completed = True
     finally: